Method of brazing parts of Ti-Al-Nb alloy

ABSTRACT

A brazing alloy-filler metal for brazing parts made of TiAlNb alloys has a brazing temperature of about 1020 DEG  to 1250 DEG  C. and a composition of, in weight percent, 37-75 titanium, 5-43 niobium, 20-58 nickel.

This application is a division, of application Ser. No. 07/207,803,filed 06/17/88 now U.S. Pat. No. 4,883,640.

This invention discloses a brazing alloy - filler metal useful injoining, for example, titanium-aluminum-niobium (TiAlNb) alloys. SuchTiAlNb alloYs are useful in the aircraft industry because they arelightweight and can withstand elevated temperatures.

A brazing alloy-filler metal in accordance with this invention comprises37-75% titanium, 5-43% niobium, 20-58% nickel, all percentages byweight, having a brazing temperature between about 1020° to 1250°Centigrade. Because the solution heat treatment temperature of theTiAlNb alloy is about 1200° C., brazing and solution heat treating canbe advantageously carried out simultaneously when the brazing alloy ofthis invention is used.

U.S. Pat. No. 3,662,455 discloses a nickel-titanium-niobium alloy formetal-to-ceramic and ceramic-to-ceramic braze bonds especially useful inthe manufacture of alkali metal vapor arc lamps. The alloy constituentslie within the following percentage weight ranges: 22.8-36.4% Ti;26.9-42.9% Ni; 20.7-50.3% Nb.

A brazing alloy-filler metal as per the instant invention is outside thedisclosure of U.S. Pat. No. 3,662,455 in titanium content. The densityof the brazing alloy as per this invention is a closer match to the lowdensity of a TiAlNb alloy than is the nickel-titanium-niobium alloydisclosed in U.S. Pat. No. 3,662,455.

Several TiNbNi alloys, as per this invention, in the form of small skullmelted buttons were placed at the ends of T joints made from 65% Ti, 14%Al, 21% Nb alloy and brazed with the following results

Brazing alloy number 5 (50 Ti, 15 Nb, 35 Ni) was brazed at 1040° C. for10 minutes with an excellent full filleted joint.

Brazing alloy number 2 (60 Ti, 15 Nb, 25 Ni) was brazed at 1100° C. for10 minutes with excellent results.

Brazing alloy number E (45 Ti, 20 Nb, 35 Ni) was brazed at 1100° C. for10 minutes with excellent results.

Brazing number M (40 Ti, 20 Nb, 40 Ni) was brazed at 1200° C. under 10⁻⁵Torr vacuum for 10 minutes with excellent results.

Brazing alloy number 6 (40 Ti, 25 Nb, 35 Ni) was brazed at 1200° C.under 10⁻⁵ Torr vacuum for 10 minutes with excellent results.Photomicrographs of the joints showed excellent alloying with littlesign of a seam. An additional 10 minutes hold time will eliminate thepresence of the original filler metal. A homogeneous joint is consideredideal because a second phase can act as a stress riser and can lead tostress induced corrosion. Table I shows the composition in weightpercent of TiNbNi alloys within this invention on which solidus andliquidus temperatures were determined.

                  TABLE 1                                                         ______________________________________                                        Sample  Ti       Nb    Ni     Sol. °C.                                                                      Liq. °C.                          ______________________________________                                        1       70        5    25     938    1050                                     2       60       15    25     938    1076                                     3       50       25    25     933    1094                                     4       60        5    35     948    1050                                     5       50       15    35     934    1020                                     6       40       25    35     958    1145                                     7       50        5    45     933    1254                                     8       40       15    45     1108   1282                                     10      55       15    30     935    1010                                     11      45       15    40     946    1171                                     D       55       10    35     937    1020                                     E       45       20    35     938    1054                                     J       60       10    30     933    1000                                     K       50       10    40     928    1160                                     L       50       20    30     937    1020                                     M       40       20    40     1076   1172                                     ______________________________________                                    

I claim:
 1. The method of joining metal parts made of a TiAlNb alloyhaving a solution heat treating temperature of about 1200° C. comprisingthe steps of disposing a brazing alloy at the joint between the parts,the brazing alloy having a brazing temperature between about 1020° C. to1250° C. and having a composition of, in weight percent, 37-75 titanium5-43 niobium, 20-58 nickel and brazing the parts at a temperature ofabout 1020° C. to 1250° C. to form a uniform fillet at the joint.
 2. Themethod of claim 1 wherein the brazing alloy has a composition of 45 Ti,20 Nb, 35 Ni.
 3. The method of claim 1 wherein the brazing alloy has acomposition of 40 Ti, 25 Nb, 35 Ni.
 4. The method of claim 1 wherein thebrazing alloy has a composition of 40 Ti, 20 Nb, 40 Ni.
 5. The method ofclaim 1 wherein the brazing alloy has a composition of 60 Ti, 15 Nb, 25Ni.
 6. The method of claim 1 wherein the brazing alloy has a compositionof 50 Ti, 15 Nb, 35 Ni.